1. Field of the Invention
The present invention relates to a light source driving apparatus for driving a light source, a display device having the light source driving apparatus and a method of driving a light source. More particularly, the present invention relates to a light source driving apparatus, which is capable of decreasing power consumption, a display device having the light source driving apparatus and a method of driving a light source.
2. Description of the Related Art
Recently, due to rapid development of data processing devices, a display device displaying images corresponding to processed data by a data-processing device has also been recently developed. Flat panel type display devices, in particular, have been developed because of their small size, light weight, full-color and realization of high resolution images compared to a cathode-ray tube (“CRT”) type display device.
Flat panel type display devices include a liquid crystal display (“LCD”) apparatus, a plasma display panel (“PDP”), an electro luminescence (EL) apparatus, etc. The LCD apparatus employed by a mobile phone, a computer monitor and a notebook computer, etc.
The LCD apparatus includes a display unit. The display unit includes an LCD panel and a driving module. The LCD panel has a screen and displays an image. The driving module provides a driving signal to the LCD panel.
The LCD panel includes a first substrate and a second substrate. The first substrate includes a thin film transistor array. The second substrate is combined with the first substrate such that a liquid crystal layer is disposed between the first and second substrates. When the driving signal is applied to electrodes formed at the first and second substrates, respectively, a respective thin film transistor of the thin film transistor array is turned on to generate an electric field between the first substrate and the second substrate. As a result, an arrangement of liquid crystal molecules of the liquid crystal layer is changed in response to the electric field applied thereto, and thus a light transmittance of the liquid crystal layer is changed to display an image.
Therefore, the LCD apparatus requires a light source unit that provides a light with a predetermined luminance to display images.
The light source unit includes a light source and optical members. The light source generates light with a predetermined luminance. The optical members improve optical characteristics of the light generated by the light source and provides the LCD panel with the light having improved characteristics.
Generally, a cold cathode fluorescent lamp (“CCFL”) may be employed as the light source. Also, a light-emitting diode may be employed as the light source.
For example, the light-emitting diode may include a plurality of light-emitting diodes emitting a red-colored light, a green-colored light and a blue-colored light, respectively, that are employed in an LCD apparatus. The LCD apparatus includes a light source driving unit driving the light-emitting diode to provide a synthesized-white light to the LCD panel by controlling luminance of the red-colored light, the green-colored light and the blue-colored light emitted from the light-emitting diodes.
Generally, when the LCD apparatus, for example, is employed in a mobile device such as a mobile phone, the light source driving unit drives the light source in a first driving mode, a second driving mode and a third driving mode.
The first driving mode may be defined as a normal-luminance driving mode. In order for the LCD apparatus employed in a mobile device to display an image at an initial driving, the light source driving unit provides a high voltage to the light-emitting diode to display an image with a normal luminance.
The second driving mode may be defined as a low-luminance driving mode, which is called a dimming mode. After the LCD apparatus is driven in the first driving mode, the light source driving unit provides a low voltage, which is lower than a voltage provided in the first driving mode. The light source driving unit provides the low voltage to the light-emitting diode according to an external signal or a sensing-signal outputted by sensing an external luminance, so that the LCD apparatus displays an image of a low luminance.
Therefore, when the LCD apparatus is driven in the second driving mode, an electric power consumed by the light source unit is reduced. As a result, power consumption of the LCD apparatus is decreased.
The third driving mode may be defined as a standby mode in which the light-emitting diode is turned off. After the LCD apparatus is driven in the second driving mode during a predetermined time, the light emitting diode is turned off in the third driving mode.
As mentioned above, according to the light source driving unit that is driven in the first to third driving modes, power consumption of the LCD apparatus is decreased compared to driving only in the first mode or first and third modes. When the LCD apparatus is applied to the mobile device using a battery with a limited electric power as a power supply device, the time of using the mobile device is increased by employing a light source driving unit that is driven in the first to third driving modes.
Generally, the mobile device, for example, such as the mobile phone, personal digital assistant (“PDA”), etc., displays image in the dimming mode to reduce power consumption. However, the light source driving unit consumes more than twice the energy compared to that consumed by the light emitting diode. Therefore, a light source driving apparatus capable of decreasing power consumption in a low-luminance driving mode is desired.